This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. UreI from H. pylori is a pH-sensitive Urea transporter. Urea is transported to induce changes in the periplasmic space pH essential for survival and reproduction in low pH environments. Thus, H. pylori is insensitive to the acidic environment of the stomach due to UreI. About 20% of UreI-mediated infections of H. pylori result in gastric or duodenal peptic ulcer disease. Following infection there is a 20-fold increase in the incidence of gastric metaplasia and gastric cancer. UreI, and homologs, have been cloned into pET101 expression vector and expressed in E. coli BL21(43) cells. Protein was solublized using 2% DDM Protein and was purified via C-terminal His tag using a cobalt (Talon) column in the presence of E. coli polar lipid extract. Site directed mutagenesis of His residues supports that the H+-sensing ability of UreI is on the periplasmic portion opposed cytosolic. Initial crystallization conditions were obtained via hanging drop vapor diffusion at 23[unreadable]C. X-ray diffraction of crystals showed they belong to the orthorhombic space group C222 and diffract to 9[unreadable]. Since there are already some compounds that inhibit UreI, delineating a high resolution structure would enable higher affinity and selectivity of chemicals that bind to UreI. This is significant because UreI would be a prime target for eradication of gastric infection and subsequent cancer initiation.